This invention relates to a combinatorial molecular layer epitaxy apparatus that is useful to form an inorganic superstructure, a metallic superstructure or an organic superstructure, especially to make an efficient search for substances in a short period of time.
The invention further relates to a combinatorial molecular layer epitaxy apparatus that permits a substrate or substrates to be conveyed in the apparatus as a thin film forming system and, to be conveyed in a state in which they remain heated, and successive processing chambers to be formed as independent vacuum chambers with pressure and temperatures therein controllable independently of one chamber from another.
At recent times, following the discovery of lanthanum/barium/copper-oxide superconductive materials, a great progress has been made of thin film forming technologies for high temperature superconducting oxides. With such a progress, efforts have been expended extensively to search for and to investigate a variety of new functional substances for metallic, inorganic and organic materials.
In the field of forming thin films of high temperature superconducting oxides, the fact that a functional oxide material such as of perovskite type is itself a multicomponent material with a plurality of oxides makes it difficult to theoretically predict an optimized component proportion and a correlation between thin film preparing conditions and resultant properties, and provides no alternative but to adopt a trial and error approach for optimization.
Under the circumstances, X. -D. Xiang et al conducted a search for oxide high temperature super-conductors on combining a multi-sputtering thin film forming process with a mask patterning technique of covering particular areas on a substrate with masks, and effecting a combinatorial synthesis of inorganic materials in which a number of inorganic substances are synthesized parallel to each other, and showed that this approach had a power in functional search for a multicomponent material (X. -D. Xiang et al, Science, 268, 1738 (1995)).
Also, G. Briceno et al in search for colossal magnetoresistance (CMR) materials, prepared from a new material: LnXMYCoO3xe2x88x92xcex4(Ln=La, Y; M=Ba, Sr, Ca, Pb) with cobalt oxide as its base component, 128 specimens with varied compositions sputter-evaporated using combinatorial synthesis and thereafter sintered in an oxygen atmosphere. And based on the measurement of magnetic resistance of those specimens, they revealed that even a multi-oxide material exhibited a maximum magnetic resistance ratio 72% CMR. Significantly, discovery and optimization of a new CoO2-based CMR material were achieved on conducting a combinatorial synthesis only twice with varied sintering conditions.
It can be seen, however, that a combinatorial synthesis referred to above for inorganic materials in which forming thin films are effected at a room temperature in either case only plays a role of simply controlling compositions. Also, no combinatorial synthesis has become a reality of thin films with a superstructure formed by epitaxial growth for each of molecular layers of materials either organic or inorganic.
On the other hand, it is noted that in a conventional thin film manufacturing system which involves a plurality of processing stages, wafers have been conveyed between different process stages by man or a robot, pressure and temperature process parameters have been set up for the individual processing stages one after another.
Especially where a wafer is required to have a clean surface, wafers must be conveyed through a conveying path that is hermetically sealed in a clean space.
Since such a conveyer is normally not adapted for high temperature wafers, however, it has been common to rely on a time consuming procedure in which hot wafers processed in a given process stage is cooled to a room temperature and then conveyed into a next process stage where they are heated to a required temperature for processing.
Further, the need to set up process parameters such as a reaction pressure and a wafer temperature one after another for the successive processing stages individually makes it unsuitable to process wafers continuously in different process stages.
Accordingly, the present invention is provided to resolve such problems met in the prior art as described, and has for its first object to provide a combinatorial molecular layer epitaxy apparatus that permits molecular layers to be formed each individually by epitaxial growth to form an inorganic, metallic or organic superstructure of such molecular layers, and that allows an efficient search for a substance to be conducted in a short period of time.
Another object of the present invention resides in providing a combinatorial molecular layer epitaxy apparatus that is capable of conveying wafers in their heated state, and permits successive processing chambers to be formed as independent vacuum chambers with pressure and temperatures therein controllable independently of one chamber from another.
In order to achieve the first object mentioned above, the present invention provides a combinatorial molecular layer epitaxy apparatus that comprises a common chamber having pressure therein controllable; one or more conveyable substrate heating units having a substrate holder for holding one or more substrates in the common chamber; and one or more process conducting chambers having pressure therein controllable and provided to correspond to the substrate heating units, the said process conducting chambers including a growth chamber which has a multiple raw material supply means for supplying raw materials onto a said substrate held by a said substrate heating unit, a gas supply means for feeding a gas onto a surface of the substrate, and an instantaneous observation means for instantaneously observing epitaxial growth of monomolecular layer for each of the layers on the substrate surface, thereby permitting growth temperature, pressure and supply of the raw materials to be controlled for each of the substrates and producing a group of substances caused each to grow epitaxially in an individual monomolecular layer and brought together in a single series of reactions for each of the substrates, systematically in accordance with indications of the instantaneous observation means.
The construction described above permits [multiple raw materials]xc3x97[multiple substrates]xc3x97[reaction parameters such as temperature, pressure and flux (rate of build-up) from gas phase] to be selected or controlled independently of one another and put together in any desired combination, and hence is capable of synthesizing or bringing together in a single series of reactions a group of substances into an epitaxial growth superlattice structure systematically controlled.
Also, in a combinatorial molecular layer epitaxial growth apparatus according to the present invention, the multiple raw material supply means preferably includes a laser molecular beam epitaxy means for vaporizing with an excimer laser beam a plurality of targets of different solid raw materials and for forming a thin film of a composition as aimed on each of the substrates.
This construction permits a limited depth of surface of a target to be momentarily vaporized and gasified and a thin film of a composition as aimed to be formed. It is possible to form a thin film, e. g., of an inorganic superstructure.
Also, in a combinatorial molecular layer epitaxial growth apparatus according to the present invention, the multiple raw material supply means may preferably include a laser molecular beam epitaxy means and a said substrates is composed of a material selected from the group which consists of xcex1-Al2O3, YSZ, MgO, SrTiO3, LaAlO3, NdGaO3, YAlO3, LaSrGaO4, NdAlO3, Y2O5, SrLaAlO4, CaNdAlO4, Si and compound semiconductors. Further, the target solid raw materials may include substances adapted to form a material selected from the group which consists of a high temperature superconductor, a luminescent material, a dielectric material, a ferroelectric material, a colossal magnetoresistance material and an oxide material.
This construction permits a target raw material to be consistently supplied to a substrate surface and makes the probability of adherence almost 1 regardless of a particular component. These features advantageously act in forming on a substrate a thin layer of monomolecular layers each individually caused to grow by epitaxial growth, of a high temperature superconductor, a luminescent material, a dielectric material, a ferroelectric material, or a colossal magnetoresistance material.
Further, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the multiple raw material supply means may preferably include a target turn table supported to be rotatable and vertically movable for carrying targets, and a masking plate means disposed between said targets and said substrates and supported to be rotatable and vertically movable. Also, the masking plate means may preferably comprise a plurality of masking plates having different masking configurations which are exchangeable in succession while epitaxial growths are effected. Further, the masking plate means may comprise a mask movable horizontally with respect to said substrates and adapted to cover and uncover either or both of a said substrate and a given area thereof with said movable mask.
This construction with the aid of a movable mask caused to move to provide the mask plate means with masking patterns permits a superlattice thin films varied in composition or laminated structure to be prepared in a plurality of given areas of a substrate.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the multiple raw material supply means may preferably comprise a laser molecular beam epitaxy means, and the instantaneous observation means may then comprise a reflex high-energy electron beam diffraction analysis means.
This construction permits providing a thin-filmed, for example, high melting point and multi-component oxide material while monitoring formation of layers each individually on epitaxial growth.
Further, a combinatorial molecular layer epitaxy apparatus according to the present invention may preferably further include a target loading lock chamber for loading targets with materials therein.
This construction permits exchanging targets in their clean state without exposing them to an environmental atmosphere.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the multiple raw material supply means may preferably comprise a gas source molecular beam epitaxy means adapted to apply and thereby to supply a flow controlled stream of a gaseous organometallic compound through a nozzle means onto each of the substrates.
This construction permits forming, e. g., a metallic or organic structure by using a gaseous material such as of an organometallic compound.
Further, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the multiple raw material supply means may preferably comprise a gas source molecular beam epitaxy means, and the instantaneous observation means may then comprise an optical means that makes observation based on any of reflectance differential spectroscopic, surface light absorbing and surface light interferometric processes.
This construction permits effecting an epitaxial thin film growth formation of a metallic or organic structure while monitoring monomolecular layers for each individual layer in growth.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the substrates may preferably be substrates composed of Si or a compound semiconductor.
This construction permits forming a metallic or organic superlattice structure of monomolecular layers each individually caused to grow epitaxially, on Si and compound semiconductor made substrates.
Further, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the substrates may preferably comprise substrates whose surfaces are made flat on an atomic level and whose outermost atomic layer is identified.
This construction provides the ability to observe RHEED oscillations that, for example, last with an extra-regularity and for a prolonged period of time, and thus permits ensuring epitaxial growth to proceed for each individual monomolecular layer
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the common chamber may preferably be provided with a substrate holder loading lock chamber for exchanging the substrate holders in a state in which a high vacuum is held therefor.
This construction permits exchanging substrates in their clean state without exposing them to an environmental atmosphere.
Further, in order to achieve the second object mentioned above, a combinatorial molecular layer epitaxy apparatus according to the present invention has a said substrate heating unit adapted for a pressure contact with a said process conducting chamber to vacuum seal the same, the substrate heating unit and process conducting chamber then together forming an independently pressure controllable vacuum chamber.
This construction permits substrates to be transferred between the process conducting chambers in their heated state and makes the vacuum chambers pressure and temperature controllable independently of one from another.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the substrate heating units may preferably be jointly adapted to be turned around and vertically moved by a carrier plate so as to be conveyed into association with said process conducting chambers in succession.
This construction permits the substrate heating units to move and turn along a given path or orbit and each to be transferred into association with a given process conducting chamber, and allows a substrate holder loaded with a number of substrates to be transferred into the process conducting chamber. It thus permits a plurality of process conducting chambers to conduct the processes in parallel.
Further, a combinatorial molecular layer epitaxy apparatus according to the present invention may preferably further include a shaft for revolution in the form of a tubular cylinder connected to an electric wiring and a service water piping outside of the common chamber and adapted to be turned and vertically moved in a state in which said common chamber means is held at vacuum, a cooling water piping disposed in a region of each of the substrate heating units and connected to the service water piping, and a carrier plate with its center disposed in coincidence with an axis of rotation of the shaft for revolution.
This construction permits a carrier plate to turn around the axis of rotation of the shaft for revolution continuously to allow the processes to be conducted in parallel, and prevents the cooling water piping for supply of cooling water into the substrate heating units and the electric wiring for power supply or a temperature monitoring thermo-couple from twisting.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the shaft for revolution has preferably attached thereto, a slip ring adapted to vacuum seal an upper end of the shaft for revolution and to connect that upper end electrically to the external electrical wiring, a cooling water sealing means for connection to the external service water piping, and a cooling water conduit means connected water tight to the cooling water sealing means and having the shaft for revolution passed therethrough coaxially to permit said shaft to rotate in a sliding contact therewith.
This construction permits the carrier plate to be vertically moved and rotated by means of the shaft for revolution without producing a twist of a cooling water piping or the electrical wiring.
Further, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the cooling water conduit means may preferably comprise an inner and an outer cooling water conduits disposed coaxially with the shaft for revolution and forming a single cooling water passage.
This construction permits supplying cooling water while holding the shaft for revolution moving vertically and rotating in its vacuum sealed state.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, a substrate heating unit may preferably include a substrate turning mechanism for rotating the substrate holder.
This construction improves temperature uniformity over a substrate by permitting the substrate holder to rotate.
Further, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the substrate heating units may preferably be turnable and each include a substrate turning mechanism that provides a rotation from a driving power for turning around the substrate heating units.
This construction permits a single driving power to be used both to turn the substrate heating units and to rotate the substrate holder.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, a substrate heating unit may preferably include a substrate turning mechanism for rotating the substrate holder in a vacuum chamber.
This construction permits a substrate heating unit and a processing chamber together to form a vacuum chamber with pressure and temperature therein controllable, yet permitting the substrate holder to be rotated.
Further, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the process conducting chambers may preferably include an annealing chamber for annealing substrates held by the substrate holder, a preheating chamber for preheating the substrates held by the substrate holder to a given temperature in a high vacuum, and a growth chamber for forming a thin film on a said substrate held by the substrate holder, and an etching chamber for etching a substrate with the thin film caused to grow and formed thereon.
This construction permits performing a plurality of processes in parallel consecutively.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the substrate holder may preferably be formed with openings each in the form of a slit, arranged to surround one or more substrates.
This construction permits reducing an escape of the amount of heat from the substrate, and thus allows the substrate to be heated uniformly and efficiently.
Further, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the substrate holder may preferably be in the form of a disk that is hollow inside and having its side wall formed with an annular groove that permits the substrate holder to be held on a substrate heating unit.
This construction permits easily loading the substrate holder into the substrate heating unit.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the substrate holder may preferably comprise a holder ring having a stepped edge inside and having its side wall formed with an annular groove that permits the substrate holder to be held on a substrate heating unit, and a holder plate in the form of a disk to be seated on the stepped edge of the holder ring for supporting one or more substrate, the disk holder plate being formed of a material that is high in heat absorbing efficiency on its side facing the substrate heating unit.
This construction that allows the holder plate heated to contact only with the stepped edge of the holder ring permits reducing escape of the amount of heat by heat conduction and hence improves temperature uniformity over the holder plate.
Further, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the holder plate formed of the material that is high in heat absorbing efficiency may preferably be constituted by an inconel plate with a surface region oxidated at a high temperature.
This construction permits effectively heating the holder plate.
Also, in a combinatorial molecular layer epitaxy apparatus according to the present invention, the substrate heating means comprises a lamp heater, the substrate holder and the holder plate being arranged to lie at a focusing position of the lamp heater.
This construction permits heat rays focused on the substrate holder and the holder plate to be effectively heated.